how to integration paypal payment gateway in codeigniter – onlinecode

<?php defined('BASEPATH') OR exit('No direct script access allowed');
class Products extends CI_Controller
{
    function  __construct() {
        parent::__construct();
        $this->load->library('paypal_lib');
        $this->load->model('product');
        $this->load->database();
    }
     
    function index(){
        $data = array();
        //get products inforamtion from database table
        $data['products'] = $this->product->getProducts();
        //loav view and pass the products information to view
        $this->load->view('products/index', $data);
    }
     
    function buyProduct($id){
        //Set variables for paypal form
        $returnURL = base_url().'paypal/success'; //payment success url
        $failURL = base_url().'paypal/fail'; //payment fail url
        $notifyURL = base_url().'paypal/ipn'; //ipn url
        //get particular product data
        $product = $this->product->getProducts($id);
        $userID = 1; //current user id
        $logo = base_url().'Your_logo_url';
         
        $this->paypal_lib->add_field('return', $returnURL);
        $this->paypal_lib->add_field('fail_return', $failURL);
        $this->paypal_lib->add_field('notify_url', $notifyURL);
        $this->paypal_lib->add_field('item_name', $product['name']);
        $this->paypal_lib->add_field('custom', $userID);
        $this->paypal_lib->add_field('item_number',  $product['id']);
        $this->paypal_lib->add_field('amount',  $product['price']);        
        $this->paypal_lib->image($logo);
         
        $this->paypal_lib->paypal_auto_form();
    }
 
     function paymentSuccess(){
 
        //get the transaction data
        $paypalInfo = $this->input->get();
           
        $data['item_number'] = $paypalInfo['item_number']; 
        $data['txn_id'] = $paypalInfo["tx"];
        $data['payment_amt'] = $paypalInfo["amt"];
        $data['currency_code'] = $paypalInfo["cc"];
        $data['status'] = $paypalInfo["st"];
         
        //pass the transaction data to view
        $this->load->view('paypal/paymentSuccess', $data);
     }
      
     function paymentFail(){
        //if transaction cancelled
        $this->load->view('paypal/paymentFail');
     }
      
     function ipn(){
        //paypal return transaction details array
        $paypalInfo    = $this->input->post();
 
        $data['user_id'] = $paypalInfo['custom'];
        $data['product_id']    = $paypalInfo["item_number"];
        $data['txn_id']    = $paypalInfo["txn_id"];
        $data['payment_gross'] = $paypalInfo["mc_gross"];
        $data['currency_code'] = $paypalInfo["mc_currency"];
        $data['payer_email'] = $paypalInfo["payer_email"];
        $data['payment_status']    = $paypalInfo["payment_status"];
 
        $paypalURL = $this->paypal_lib->paypal_url;        
        $result    = $this->paypal_lib->curlPost($paypalURL,$paypalInfo);
         
        //check whether the payment is verified
        if(preg_match("/VERIFIED/i",$result)){
            //insert the transaction data into the database
            $this->product->storeTransaction($data);
        }
    }
}
?>